Bone conduction audiphone



July 11, 1939. KOCH BONE CONDUCTION AUDIPHONE Filed July 5, 1954 INVENTOR @atentei tints E in states I arcane arcane e i none ocnnnorron annmnonn Henry Koch, .l'amaica, N. Y assignor to Dictm graph Products Company, inc, Jamaica, N. $2, a corporation of Delaware Applicatiohduly 5,1934, Serial No. 733,739

5 Claims. (cl. 179-1437) This invention relates to audiphones and has particular reference to audiphones of the type in which sound vibrations are conducted through the bone structure of the user to the inner ear instead of through the outer ear by air vibration;

In my copending application Serial No. 678,130,

filed June 29, 1933, there is described a bone conduction receiver which is characteristic in that the vibratory member includes a casing which is held in operative connection with the bone structure of the user and transmits the audioirequency vibrations imposed upon it by an electromagnetic means directly to the inner ear of the user through the bone. The electromagnetic means is supported by the vibratory member within the casing and the magnet thereof is of such mass that it has greater inertia than the vibratory member and accordingly the vibratory member, in effect, vibrates in respect to the electromagnetic system according to the inertia or reaction principle. With this arrangement the air gap of electromagnetic means between the magnet and the reed or tympanum, which forms part of the vibratory member, remains constant at all times, subject to the auditory vibrations, no matter what pressure is applied to the vibratory member, because the electromagnetic means is carried by the vibratory member and any movement of the vibratory member is accompanied by an equal movement of the electromagnetic means.

It is desirable to-make the air gap adjustable and the present invention is concerned with an arrangement whereby the air gap may be adjusted at will to vary the response characteristics of the audiphone to suit various conditions of use. Also, with the new arrangement, the resiliency of the metal forming the reed of the vibratory member and heretofore employed to support the magnet is'not relied upon, but a separate spring support-for the magnet is provided and is of such structure as to retain its resiliency under all normal operating conditions and not be subject to variations in its resiliency due to changes in temperature or fatigue of the metal constituting it.

The invention comprises a vibratory member including a casingfone surface of which is adapted to be placed in operative connection with the bone structure of the user, such as upon the mastoid eminence behind the ear of the user, and having as an element the reed or tympanum which is vibrated in accordance with frequencies substantially throughout the audible frequency -range by an electromagnet carried by the vibratory member and enclosed within the casing.

cantilever spring with the The electromagnet is preferably mounted upon" the tympanum or reed by two spring steel strips, one of which has greater flexibility than the other and is secured to one end of a massive permanent magnet extending'parallel to the reed or I tympanum and carrying at its free end the voice coil, the end of whose core forms the air gap' with the corresponding end of the reed or tympanum. The other spring steel strip is anchored at one end on the reed or tympanum and extends cantilever-fashion parallel to the permanent magnet' and the reed or tympanum and between them.

An adjusting screw connects the free end of this permanent magnet 'so that by adjusting this screw, the free end'offthe permanent magnet carrying the voice coil'may be adjusted with respect to the reed or tympanum to vary the air gap at will, so that the response characteristics of the devicemay be adjusted. The necessary flexibility betweenthe electromagnet and the reed or tympanum-which permits the vibration in response to the audlo frequency currents traversing the voice coil, is afforded by. the two spring steel strips, whose stiffness is such as to prevent freezing at the air gap.

.It will be seen that the new bone conduction' receiver of this invention is adjustable to'suit the characteristics of the individual user and that by means of this adjustment any manufacturing irregularities can be compensated for to secure uniform operating results consistent with any adjustment desirable to conform to the user's requirements. Also, the use of spring steel forthe support of the electromagnetic system renders the device immune to deterioration because of metal fatigue resulting from rapid vibration of the device and also eliminates variation in the response characteristics of the device due to temperature changes.

For a more complete understanding of the invention reference may be had to the accompanying drawing in which Figure 1 is an enlargedlongitudinal section through the bone conduction receiver of this invention as seen along the line l-| of Figure 2;

Figure 2 is a transverse section through the receiver as seen along the line 2-2 of Figure 1; and

Figure 3 is a perspective view illustrating the manner in which the receiver is supported for use on ahead band or the like.

Referring to the drawing, numeral l0 designates the casing of the receiver A, and this casing. is formed of substantially non-resonant material, such as hard-rubber, a synthetic resin, or the like, and includes the face plate I l secured thereto by screws l2 and also forming the contact plate which is placed in operative connection with the bone structure of theuser.

A pair of terminal strips i3 are inlaid flush with the inner surface of face plate H, and areprovided at their inner ends with terminals l4 and at their outer ends with contact plates l6, which, when the face plate ii is secured in place on casing ID, are electrically connected to contacts l6 through springs l1. Contact pins l8 on the ends oi the flexible conductor l9 connected in the listening circuit of the audiphone make electrical connection with contacts l6 when they are inserted in the sockets 20 into which the contacts l6 project.

Rigidly secured to the inner surface of face plate H by means of screws 2| is a stiff tympanum or reed 22. Alternatively, the reed need not be inherently stiff but will be rendered stiff by the 'rigid connection between it and the stifl face plate A boss 23 is formed on one end of tympanum or reed 22 and to this boss 23 is secured by screw 24 and washer 25 an upstanding flexible strip 26 of spring steel or other resilient material having a substantial degree of flexibility. Rigidly secured to the free end of strip 26 by means of bolt 21 and washer 28 is a bar magnet 29 of considerable mass so that it has greater inertia than the tympanum or reed 22 and its appurtenant parts. Secured to the free end of bar magnet 29 by means of bolt 30 is a pole piece 3| the free end of which forms, with the corresponding surface of the reed or tympanum 22, the air gap 32.

Mounted on pole piece 3| is a voice coil 33, the terminals 34 of which are connected to the corresponding terminals l4 of the contact strips l3. The voice coil 33 is accordingly connected in the listening circuit of the audiphone and, when energized by currents varying in accordance with frequencies substantially throughout the audible range,eflectsvibration of the reed or tympanum 22 in accordance with the well-known electromagnetic phenomenon,

Secured cantilever-fashion by screws 35 to the boss 23, so as to extend substantially parallel to and between tympanum or reed 22 and bar magnet 29, is a stiff spring 36 of spring steel or other resilient material. The free end of the cantiliver spring 36 is provided with an aperture through which passes a bolt 31 rigidly secured to the bar magnet 29 intermediate its ends. A pair of nuts 36 and 39 on the bolt 31 and located at opposite sides of cantilever spring 36 determine the relationship between spring 36 and bar magnet 29 and consequently between tympanum or reed 22 and bar magnet 29. Accordingly, by adjusting this relationship, the width of the air gap 32 may be varied at will, preferably between twoand four-thousandths of an inch.

It will be seen that the two nuts 38 and 39 serve as luck nuts with respect to each other, so that an adjustment of the air gap when once made remains fixed except as it is varied by the vibrations of the reed or tympanum 22. It will also be seen that although cantilever spring 36 is flexible, spring strip 26 has a much greater flexibility, so that any adjustment of the air gap in the manner described results in a proportionate bending of strip 26. Thus, both strips 26 and 36 contribute to the resilient support of the bar magnet 29 and flex sufliciently to permit the vibration of the reed or tympanum 22 in response to varying currents traversing the voice coil 33. At the same time, the resilient support for the bar magnet 29 afl'orded by spring strips 26 and 36 is sufliciently stifl to secure a powerful vibration of the tympanum or reed 22 without permitting freezing between pole piece 3| and the reed or tympanum 22.

The operation of the new receiver of this invention will be understood from the 'foregoing description and in use the receiver A is nonrigidly supported, such as by 3. fork 46 embracing the casing l0 and pivotally connected thereto by pins 4| inserted in corresponding apertures in the sides of casing III. A head band 42 may be secured at one end to fork 40, so that when the head band 42 is placed on the head of the user the face or contact plate ll of the receiver A is firmly held in operative connection with the bone structure of the head of the user, such as on the mastoid eminence-behind the car.

It will be observed that inasmuch as the casing A is supported by the head band 42, and the electrornagnetic means, comprising tympanum or reed 22, the bar magnet 29 and the voice coil 33, is supported by the face or contact plate H which serves as the vibratory member, no forces are applied by the head band 42 directly to the electromagnetic means. Accordingly, the air gap 32 is not varied by the pressureapplied to the face or contact plate Ii or any other part of the casing I 0 when the receiver is in use.

Also, because of this construction and the inertia of the bar magnet 29 compared to that of the vibratory member, comprising the face or contact plate II, the casing l0 and the tympanum or reed 22, the vibratory member, in effect, vibrates relatively to the massive permanent magnet 29 according to the reaction or inertia principle. By adjusting the air gap 32 by means of nuts 39 and 39, the response characteristics of the receiver may be varied at will.

Furthermore, the spring steel strips 26 and 36 which support, the bar magnet 20 are not subject to variations in their resiliency due to metal fatigue or changes'in temperature, so that the response characteristics of the receiver remain constant under all normal operating conditions and for an indefinite period of time.

The pitch of the receiver may also be adjusted in a simple way to suit the characteristics of the user, either by substituting a stiffer or less still spring for spring strip 36, or by starting with a stiff spring 36 and grinding or filing it thinner at some point intermediate its ends to obtain a selected degree of flexibility. Also the length of the spring 36 may be varied to obtain the same result.

It will be seen that the new instrument contains all of the means whereby adjustment may be made to secure for the user the best possible response consistent with his individual requirements, and that despite the use of a massive magnet to secure the reactive action desired, the tone of the instrument is not suppressed but is clear and sharp because the magnet is balanced intermediate its ends by the bolt 31.

While the present invention has been described in connection with an audiphone receiver, it is to be understood that the invention is not limited to that use, but may be applied to other uses within the scope of this invention.

I claim:

1. In an audiphone, the combination of 2. casing, a vibratory member carried by the casing and including a reed, a permanent magnet having a voice coil, a pair of resilient members disposed at an angle to each other for supporting the magnet in operative relation with the reed to form an air gap between them, and means for adjusting the relationship between at least one of said members and the magnet to vary the said air gap.

2. In an audiphone, the combination of a vibratory member including a reed, a permanent magnet having a voice coil, a resilient member supporting the magnet at one end to form an air gap between the reed and the other end of the magnet, a second resilient member supporting the magnet intermediate its ends, and an adjustable connection between the second member and the magnet for varying the air gap.

3. In an audiphone, the combination of a vibratory member including a reed, a bar magnet having a voice coil, a spring strip connecting only one end of the magnet to the reed, said reed and magnet being arranged in substantially parallel relation, 9. second spring strip anchored at one end to the reed and extending between the magnet and the reed, and an adjustable connection between the other end of said second spring strip and said magnet intermediate the ends of the latter for varying the relation between the magnet and the reed.

4. In an audiphone, the combination of a vibratory member including a reed, a bar magnet having a voice coil, a spring member connected at one end to the reed and extending substantially parallel to the reed in spaced relation thereto, a connection between the other end of said spring member and a point intermediate the ends of the magnet for supporting the magnet in operative relation to the reed to form an air gap between the reed and the free end of the magnet, and means for adjusting said connection to vary'the air gap.

5. In an audiphone, the combination 01' a sub-- stantially flat reed, a permanent bar magnet, a speech coil and a pole piece on one end thereof, a non-rigid strip secured to the opopsite end of the magnet and to one end of the reed tor spacing the reed and pole piece to form a narrow air gap, means extending between the reed and the magnet and connected to the latter intermediate its end for flexing the strip to vary the said air HENRY KOCH. 

